In general, abrasive products are known to have abrasive particles adherently bonded to a sheet-like backing. It is generally known to stratify the abrasive particles and binders, such as in coated abrasive articles, in such a way as to basically segregate the abrasive particles between an underlying binder and an overlaying binder.
More typically, abrasive products have a backing substrate, abrasive particles, and a binder which operates to bond or hold the abrasive particles to the backing. For example, a typical coated abrasive product has a backing that is first coated with a binder, commonly referred to as a "make coat", and then the abrasive particles are applied to the make coat. The application of the abrasive particles to the make coat typically involves electrostatic deposition or a mechanical process which maximizes the probability that the individual abrasive particles are positioned with their major axis oriented perpendicular to the backing surface. As so applied, the abrasive particles optimally are at least partially embedded in the make coat that is then generally solidified or set (such as by a series of drying or curing ovens) to a state sufficient to retain the adhesion of abrasive particles to the backing.
Optionally, after precuring or setting the make coat, a second binder, commonly referred to as a "size coat", can be applied over the surface of the make coat and abrasive particles, and, upon setting, it further supports the particles and enhances the anchorage of the particles to the backing. Further, a "supersize" coat, which may contain grinding aids, anti-loading materials or other additives can be applied over the cured size coat. In any event, once the size coat and supersize coat, if used, has been cured, the resulting coated abrasive product can be converted into a variety of convenient forms such as sheets, rolls, belts, and discs.
Coated abrasives are used to abrade a variety of workpieces including metal, metal alloys, glass, wood, paint, plastics, etc. In abrading certain workpieces, for example, wood, paint, and plastics, the coated abrasive has a tendency to "load". "Load" or "loading" are terms used in the industry to describe the debris, or swarf, that is abraded away from the workpiece surface that subsequently becomes lodged between the abrasive particles of the abrasive article. Loading is generally undesirable because the debris lodged between abrasive particles inhibits the cutting ability of the abrasive article.
On solution to the loading problem is to apply a supersize coating over the size coating. For example, U.S. Pat. No. 2,768,886, describes a metal stearate supersize coating that may reduce the amount of loading. Metal stearate supersize coatings have been employed in coated abrasive articles that are designed to abrade paint and lacquer type coatings. However, metal stearate supersize coatings may not be effective in some abrading operations. For example, wood and wood-like materials (such as particle board and pressboard) are typically abraded with coated abrasive belts. These coated abrasive belts typically operate at higher abrading speeds and pressures than coated abrasive discs or sheets. As a result, a metal stearate supersize is worn away from the coated abrasive belt in a relatively short period of time. The end result is that the metal stearate supersize may be effective at reducing loading in a coated abrasive belt but the supersize life is essentially so short so as to be ineffective.
Loading is a serious problem in the area of wood sanding. In many applications, coated abrasive articles tend to load with the sawdust that is abraded away from the wood or wood-like surface. This loading typically leads to burning of the sawdust at the interface between the surface of the abrasive article and the surface of the wood workpiece adjacent to the abrasive article. If sawdust burning does occur, this can lead to damage to the underlying wood workpiece. Additionally, loading reduces the effective work life of the coated abrasive article.
Thus, what is desired in the industry is a load resistant coating for abrasive articles that can be used under relatively high abrading pressures and relatively high abrading speeds.